Machinery must often apply power generated by an engine or motor to a purpose such as drilling a hole or turning a wheel. As such, the machinery must transfer mechanical power. Mechanical power is transferred by rotating elements such as shafts, plates, and gears. For example, in a car the power generated by the engine must be transferred to the wheels. Most car engines generate power that is available on a rotating shaft called the crankshaft. The crankshaft is connected to a transmission via a clutch. A clutch effects rotary power transfer by adjusting the friction between two plates. Forcing a spinning plate's face against another plate's face causes power transfer or loss at the interface.
Sometimes a viscous fluid resides between the plate faces, which are specially formed or textures, such that power is transferred without the plates actually touching. A transmission adjusts the power by transferring it through a set of gears. The power then proceeds via more rotating elements, such as shafts, plates and gears, to the wheels where it supplies motive force. Car wheels themselves may be viewed as rotating gears that transfer power to the surface of the earth.
People often desire to know how much power the engine produces. They also want to know how much power each rotating element transfers and how much power is available at the wheels because some power is lost in the transfer from engine to earth. Any machine that similarly transfers mechanical power to a purpose has similar losses. Rotational mechanical power can be calculated as a function of torque and speed.
Torque is a force applied to cause rotation. For example, someone can try to turn a bolt with a 1 foot (ft.) wrench by placing one end of the wrench on the bolt and pushing the other end with 100 pounds (lbs.) of force. In this example, that person has applied 100 ft.-lbs of torque. Torque is a well-known concept to those skilled in any of the arts of engines, motors or mechanical power transfer.
Torque can be measured in a variety of ways. One way is to measure the flex or strain of a rotating element, such as a rotating shaft. Whenever power is transferred along a shaft, the shaft will flex. If more power is transferred, then the shaft flexes more. Sometimes, part of the shaft is designed specially for torque measurements. A short length of the shaft can be made thinner so it flexes more. A short length of the shaft can be made of a material that flexes differently than the material used for the rest of the shaft. Instead of a section that is thinned or a different material, an apparatus that reacts to the torque can be used. Regardless of any special properties or sections of the shaft, the flex is measured.
One of the many different conventional techniques for measuring the flex involves measuring the stress, or strain, on the shaft. U.S. Pat. No. 6,631,646 discusses, for example, an apparatus for measuring strain. Another technique involves measuring the relative rotational offset between two sections of the shaft. U.S. Pat. No. 6,817,528, for example, discusses an apparatus for measuring the relative rotational offset between two rotating members. The torque on gears and plates can also be measured because they also flex when under the influence of torque.
Furthermore, the torque on a rotating element can be measured anywhere on the rotating element because when a rotating element flexes, the entire rotating element flexes. For example, a flange can be attached to a shaft or can be formed as part of the shaft. A torque sensor on the flange can be used to measure the torque on the shaft. Those skilled in any of the arts of engines, motors, or mechanical power transfer know these and many other ways of measuring the torque applied to a rotating element.
Speed is simply how fast something is going. Rotational speed is how fast something is spinning and is often measured as rotations per minute (rpm). One way to measure rotational speed is to count how many times a target mounted on a rotating element passes a stationary sensor per unit of time. Another method is to power an electric generator at a speed directly proportional to that of a rotating element, typically via a mechanical linkage such as a belt or gear, such that the voltage produced is a function of rotating element's speed. Those skilled in any of the arts of engines, motors, or mechanical power transfer know these and many other ways of measuring rotational speed.
Torque and speed can be either measured using sensors or targets attached to rotating elements. There are many kinds of rotating elements. Shafts, gears, plates, belts, wheels, flywheels, pulleys, and cables are examples of rotating elements. The common property of all rotating elements is that they rotate. Those skilled in any of the arts of engines, motors, or mechanical power transfer know these and many other types of rotating elements.
Power refers to the amount of energy that can be produced, delivered, or consumed in a certain amount of time. The power transferred by a rotating element is proportional to the element's rotational speed multiplied by the torque on the element. The following equation (1) can be utilized to calculate power:power(hp)=speed(rpm)*torque(ft-lbs)/5252   (1)
Where the speed is in rotations per minute, torque is in foot-pounds, and power is in horsepower. Accurate measurements of the power transferred by a rotating element require accurate measurements of both speed and torque.
Heavy equipment and other large machines often incorporate sensors for measuring speed and torque. In general, these machines perform torque sensing in one module and speed sensing in another module. This is because of the size of the machine and the view that torque sensing is functionally different and separate from speed sensing. Additionally, torque sensing has customarily involved special hardware and foresight in machine design whereas speed sensing can be incorporated as an inexpensive afterthought. As a result, measurements of power have been available, but only as the result of a calculation derived from one measurement from a speed sensing module and another measurement from a torque sensing module.
Many applications, such as automotive, rarely have power measurements available because they are extremely price sensitive. The current solutions for power measurements are not appropriate for automotive engine, transmission, and drive train applications. There are many similar cost sensitive applications for which an adequate way to measure power does not exist.
Most sensors require wires that carry signals and power. Electrical power enables a sensor to operate. Input signals generally carry control information such as synchronization or operational commands to the sensor. Output signals generally carry sensor readings, diagnostics, or other information to external circuitry. Some sensors are battery powered and receive control signals and transmit output signals wirelessly. A sensor with low enough power requirements can be powered wirelessly. Such sensors often receive power and input signals and transmit output signals via inductive coupling.
The embodiments disclosed herein therefore directly address the shortcomings of conventional systems and devices by combining a torque sensor and a speed sensor into a single power sensor module that is suitable for many price sensitive applications.